The present invention relates to humanized monoclonal antibodies and fragments or derivatives thereof which specifically bind tumor-associated glycoprotein TAG-72, a human pancarcinoma antigen expressed by various human tumor cells. More specifically, the present invention relates to humanized monoclonal antibodies and fragments or derivatives thereof derived from murine monoclonal antibody CC49 or other murine antibodies which specifically bind TAG-72. The present invention further relates to methods for producing such humanized monoclonal antibodies specific to TAG-72, pharmaceutical and diagnostic compositions containing such humanized monoclonal antibodies, and methods of use thereof for the treatment or diagnosis of cancer.
The identification of antigens expressed by tumor cells and the preparation of monoclonal antibodies which specifically bind such antigens is well known in the art. Anti-tumor monoclonal antibodies exhibit potential application as both therapeutic and diagnostic agents. Such monoclonal antibodies have potential application as diagnostic agents because they specifically bind tumor antigens and thereby can detect the presence of tumor cells or tumor antigen in an analyte. For example, use of monoclonal antibodies which bind tumor antigens for in vitro and in vivo imaging of tumor cells or tumors using a labeled form of such a monoclonal antibody is conventional in the art.
Moreover, monoclonal antibodies which bind tumor antigens have well known application as therapeutic agents. The usage of monoclonal antibodies themselves as therapeutic agents, or as conjugates wherein the monoclonal antibody is directly or indirectly attached to an effector moiety, e.g., a drug, cytokine, cytotoxin, etc., is well known.
Essentially, if the monoclonal antibody is attached to an effector moiety the monoclonal antibody functions as a targeting moiety, i.e. it directs the desired effector moiety (which typically possesses therapeutic activity) against a desired target, e.g., a tumor which expresses the antigen bound by the monoclonal antibody. In contrast, when the monoclonal antibody itself operates as a therapeutic agent, the antibody functions both as a targeting moietyxe2x80x94i.e., it will specifically bind a cell which expresses the antigenxe2x80x94and as an effector which mediates therapeutic activity, typically tumor cell Iysis. Such effector functionsxe2x80x94including, e.g., antibody-dependent cellular cytotoxicity (ADCC) and complement dependent cytotoxicity (CDC), among othersxe2x80x94are effected by the portion of the antibody molecule generally referred to in the literature as the Fc portion. One specific tumor antigen against which various monoclonal antibodies have been developed is tumor-associated glycoprotein TAG-72. TAG-72 is expressed on the surface of various human tumor cells, such as the LS174T tumor cell line (American Type Tissue Collection (ATCC) No. CL188, a variant of cell line LS180 (ATCC No. CL187)), a colon adenocarcinoma line. Various research groups have reported the production of monoclonal antibodies to TAG-72. See, e.g., Muraro et al., Cancer Res., 48:4588-4596 (1988); Johnson et al., Cancer Res., 46:850-857 (1986); Molinolo et al., Cancer Res., 50:1291-1298 (1990); Thor et al., Cancer Res., 46:3118-3127 (1986); EP 394,277 to Schlom et al. (assigned to the National Cancer Institute); and U.S. Pat. No. 5,512,443 to Jeffrey Schlom et al. Specific antibodies to TAG-72 which are publicly available include CC49 (ATCC No. HB 9459), CC83 (ATCC No. HB 9453), CC46 (ATCC No. HB 9458), CC92 (ATCC No. HB 9454), CC30 (ATCC No. HB 9457), CC11 (ATCC No. 9455), and CC15 (ATCC No. HB 9460).
One example thereof, CC49, is a murine monoclonal antibody of the IgG1 isotype. This monoclonal antibody is a second generation monoclonal antibody prepared by immunizing mice with TAG-72 purified using the first generation antibody B72.3. Colcher et al., Proc. Natl. Acad. Sci. USA, 78:3199-3203 (1981). CC49 specifically binds TAG-72, and has a higher antigen-binding affinity than B72.3. Muraro et al., Cancer Res., 48:4588-4596 (1988). This monoclonal antibody has been reported to target human colon carcinoma xenografts efficiently, and to reduce the growth of such xenografts with good efficacy. Molinolo et al., Cancer Res., 50:1291-1298 (1996); Colcher et al., J. Natl. Cancer Inst., 82:1191-1197 (1990). Also, radiolabeled CC49 has been reported to exhibit excellent tumor localization in several ongoing clinical trials.
However, while murine antibodies have applicability as therapeutic agents in humans, they are disadvantageous in some respects. Specifically, murine antibodies, because of the fact that they are of foreign species origin, may be immunogenic in humans. This may result in a neutralizing antibody response (human anti-murine antibody (HAMA) response), which is particularly problematic if the antibodies are desired to be administered repeatedly, e.g., in treatment of a chronic or recurrent disease condition. Also, because they contain murine constant domains they may not exhibit human effector functions.
In an effort to eliminate or reduce such problems, chimeric antibodies have been disclosed. Chimeric antibodies contain portions of two different antibodies, typically of two different species. Generally, such antibodies contain human constant regions and variable regions of another species, typically murine variable regions. For example, some mouse/human chimeric antibodies have been reported which exhibit binding characteristics of the parental mouse antibody, and effector functions associated with the human constant region. See, e.g.: U.S. Pat. No. 4,816,567 to Cabilly et al.; U.S. Pat. No. 4,978,745 to Shoemaker et al.; U.S. Pat. No. 4,975,369 to Beavers et al.; and U.S. Pat. No. 4,816,397 to Boss et al. Generally, these chimeric antibodies are constructed by preparing a genomic gene library from DNA extracted from pre-existing murine hybridomas. Nishimura et al., Cancer Res., 47:999 (1987). The library is then screened for variable region genes from both heavy and light chains exhibiting the correct antibody fragment rearrangement patterns. Alternatively, cDNA libraries are prepared from RNA extracted from the hybridomas and screened, or the variable regions are obtained by polymerase chain reaction. The cloned variable region genes are then ligated into an expression vector containing cloned cassettes of the appropriate heavy or light chain human constant region gene. The chimeric genes are then expressed in a cell line of choice, usually a murine myeloma line. Such chimeric antibodies have been used in human therapy.
Moreover, the production of chimeric mouse-human antibodies derived from CC49 and CC83, which specifically bind TAG-72, has been reported. In this regard, see e.g., EPO 0,365,997 to Mezes et al. (The Dow Chemical Company). One such chimeric CC49 antibody is that produced by the cell line deposited as ATTC No. HB 9884 (Budapest).
Also, Morrison et al. report the preparation of several antitumor chimeric monoclonal antibodies, in Important Advances in Oncology, Recombinant Chimeric Monoclonal Antibodies, pp. 3-18 (S. A. Rosenberg, ed., 1990) (J. B. Lippincott, Philadelphia, Pa.). Results of clinical trials with chimeric cMAb-17-1A in patients with metastatic colorectal carcinoma now show that this antibody has a 6-fold longer circulation time and significantly reduced immunogenicity as compared to the murine monoclonal antibody from which it was derived. LoBuglio et al., Proc. Natl. Acad. Sci. USA, 86:4220-4224 (1989); Meredith et al., J. Nucl. Med., 32:1162-1168 (1991).
However, while such chimeric monoclonal antibodies typically exhibit lesser immunogenicity, they are still potentially immunogenic in humans because they contain murine variable sequences which may elicit antibody responses. Thus, there is the possibility that these chimeric antibodies may elicit an anti-idiotypic response if administered to patients. Saleh et al., Cancer immunol. Immunother., 32:185-190 (1990).
For example, when cB72.3(xcex34) was administered to patients with colorectal carcinomas, 62% of such patients elicited a human antimurine antibody (HAMA) response, which included an anti-V-region response. This is disadvantageous because a HAMA response would make repeated antitumor antibody administration potentially ineffective because of an increased antibody clearance from the serum (Saleh et al., Cancer Immunol. Immunother., 32:180-190 (1990)) and also because of potential allergic reactions (LoBuglio et al., Hybridoma, 5:5117-5123 (1986).
A number of genetic variants of potential clinical utility have been developed from MAb CC49. These include cCC49, a CH2 domain-deficient cCC49 (Slavin-Chiorini et al., Int. J. Cancer, 53:97-103 (1993)), and a single chain Fv (sFv) (Milenic et al., Cancer Res., 51:6365-6371 (1991); Sawyer et al., Protein Eng., 7:1401-1406 (1994)). These molecules may elicit relatively reduced HAMA responses in patients, since they have shown more rapid plasma and whole body clearance rates in mice and rhesus monkeys, as compared to intact IgG. Slavin-Chiorini et al. (1993) (id.); Milenic et al. (1991) (id.). Additionally, novel single-chain immunoglobulin (SClg) molecules derived from cCC49 have been reported and are encoded by single-gene constructs. One such molecule, SCIgxcex94CH1 consists of CC49 sFv linked to the human xcex31 Fc region (Shu et al., Proc. Natl. Acad. Sci. USA, 90:7995-7999 (1993)) while the other SCIg-IL-2 carries a human interleukin-2 (IL-2) molecule genetically attached to the carboxyl end of the Fc region of SCIgxcex94CH1 (Kashmiri et al., Proc. XVI Intl. Cancer Cong., 1:183-187 (1994)). Both SCIgs are comparable to cCC49 in antigen binding and antibody cellular cytolytic activity. The biological activity of the IL-2 is also retained in SCIg-IL-2.
In an effort to alleviate the immunogenicity concerns of chimeric and murine antibodies, the production of xe2x80x9chumanizedxe2x80x9d antibodies is also known. Ideally, xe2x80x9chumanizationxe2x80x9d results in an antibody that is non-immunogenic in humans, with substantially complete retention of the antigen-binding properties of the original molecule. In order to retain all the antigen-binding properties of the original antibody, the structure of its combining-site has to be faithfully reproduced in the xe2x80x9chumanizedxe2x80x9d version. This can potentially be achieved by transplanting the combining site of the nonhuman antibody onto a human framework, either (a) by grafting only the nonhuman CDRs onto human framework and constant regions with or without retention of critical framework residues (Jones et al., Nature, 321:522 (1986); Verhoeyen et al., Science, 239:1539 (1988)); or (b) by transplanting the entire nonhuman variable domains (to preserve ligand-binding properties) but also xe2x80x9ccloakingxe2x80x9d them with a human-like surface through judicious replacement of exposed residues (to reduce antigenicity) (Padlan, Molec. Immunol., 28:489 (1991)).
Essentially, humanization by CDR grafting involves transplanting only the CDRs onto human fragment and constant regions. Theoretically, this should substantially eliminate immunogenicity (except if allotypic or idiotypic differences exist). Jones et al., Nature, 321:522-525 (1986); Verhoeyen et al., Science, 239:1534-1536 (1988); Riechmann et al., Nature, 332:323-327 (1988). While such a technique is effective in some instances, CDR-grafting sometimes does not yield the desired result. Rather, it has been reported that some framework residues of the original antibody may also need to be preserved in order to preserve antigen binding activity. Riechmann et al., Nature, 332:323-327 (1988); Queen et al., Proc. Natl. Acad. Sci. USA, 86:10023-10029; Tempest et al., Biol. Technology, 9:266-271 (1991); Co et al., Nature, 351:501-502 (1991)).
As discussed, in order to preserve the antigen-binding properties of the original antibody, the structure of its combining site must be faithfully reproduced in the humanized molecule. X-ray crystallographic studies have shown that the antibody combining site is built primarily from CDR residues, although some neighboring framework residues have been found to be involved in antigen binding. Amit et al., Science, 233:747-753 986); Colman et al., Nature, 326:358-363 (1987); Sheriff et al., Proc. Natl. Acad. Sci. USA, 84:8075-8079 (1987); Padlan et al., Proc. Natl. Acad Sci. USA, 86:5938-5942 (1989); Fischmann et al., J. Biol. Chem., 266:12915-12920 (1991); Tulip et al., J. Molec. Biol., 227:122-148 (1992). It has also been found that the structures of the CDR loops are significantly influenced by surrounding framework structures. Chothia et al., J. Molec. Biol., 196:901-917 (1987); Chothia et al., Nature, 342:877-883 (1989); Tramomonteno et al., J. Molec. BioL, 215:175-182 (1990).
Small but significant differences in the relative disposition of the variable light chain (VL) and variable heavy (VH) domains have been noted (Colman et al., Nature, 326:358-363 (1987)) and those differences are ostensibly due to variations in the residues involved in the interdomain contact (Padlan et al., Molec. Immunol., 31:169-217 (1994)).
Furthermore, structural studies of the effect of the mutation of interior residues, in which changes in side chain volume are involved, have shown that the resulting local deformations are accommodated by shifts in side chain positions that are propagated to distant parts of the molecular interior. This suggests that during humanization the interior residues in the variable domains and in the interface between these domains, or at least the interior volumes, should also be maintained; a humanization protocol in which an interior residue is replaced by one of different physical properties (such as size, charge, or hydrophobicity, etc.), could result in a significant modification of the antigen combining site structure.
One method of identifying the framework residues which need to be preserved is by computer modeling. Alternatively, critical framework residues may potentially be identified by comparing known antibody combining site structures (Padlan, Molec. Immun., 31(3):169-217 (1994)).
The residues which potentially affect antigen binding fall into several groups. The first group comprises residues that are contiguous with the combining site surface and which could therefore make direct contact with antigens. They include the amino-terminal residues and those adjacent to the CDRs. The second group includes residues that could alter the structure or relative alignment of the CDRs either by contacting the CDRs or the opposite chains. The third group comprises amino acids with buried side chains that could influence the structural integrity of the variable domains. The residues in these groups are usually found in the same positions (ibid.) according to the adopted numbering system. See Kabat et al., Sequences of Proteins of Immunological Interest, NIH Pub. No. 91-3242 (5th ed., 1991) (U.S. Dept. Health and Human Services, Bethesda, Md.) and Genbank.
However, while humanized antibodies are desirable because of their potential low immunogenicity in humans, their production is unpredictable. For example, sequence modification of antibodies may result in substantial or even total loss of antigen binding affinity, or loss of binding specificity. Alternatively, xe2x80x9chumanized antibodiesxe2x80x9d may still exhibit immunogenicity in humans, irrespective of sequence modification.
Thus, there still exists a significant need in the art for novel humanized antibodies to desired antigens. More specifically, there exists a need in the art for humanized antibodies specific to TAG-72, because of their potential as immunotherapeutic and immunodiagnostic agents.
Toward this end, it is an object of the invention to provide humanized antibodies which are specific to human TAG-72.
More specifically, it is an object of the invention to provide humanized antibodies derived from murine antibodies to TAG-72, and in particular from CC49, a specific murine antibody which binds to TAG-72.
It is also an object of the invention to provide pharmaceutical compositions containing humanized antibodies which are specific to TAG-72. It is a more specific object of the invention to provide pharmaceutical compositions containing humanized antibodies derived from CC49, a murine antibody which specifically binds to TAG-72.
It is another specific object of the invention to provide methods of using humanized antibodies to TAG-72 for treatment of cancers which express TAG-72, in particular human colon cancer.
It is another object of the invention to provide immunodiagnostic compositions for detecting cancer cells which contain a humanized antibody which specifically binds TAG-72, and preferably is derived from CC49, which antibody is in labeled or unlabeled form. It is another object of the invention to provide a method of immunodiagnosis of cancer using compositions which contain a humanized antibody which specifically binds TAG-72, which is in labeled or unlabeled form.
It is still another object of the invention to provide nucleic acid sequences which encode for humanized antibodies to TAG-72 or fragments thereof. It is a more specific object of the invention to provide nucleic acid sequences which encode humanized antibodies derived from CC49, a murine antibody which specifically binds to TAG-72. It is another object of the invention to provide vectors from which may be expressed humanized antibodies to TAG-72, in particular humanized antibodies derived from CC49, a murine antibody which specifically binds to TAG-72.